Re: Weak types ?

["Juan J. Quintela" <quintela@dc.fi.udc.es>]

Pierre CASTERAN <Pierre.Casteran@labri.u-bordeaux.fr> wrote:

> let toto =
>   let id x = x
>   in id id;;
> (*
>  val toto : '_a -> '_a = <fun>
>              ^      ^
> 
>              why not " 'a " ?  
>              
> *)

Hi,
	I really dont remember the reason, but I remember one solution,
to put explicity the varibles in the binbidng, i. e.:

# let toto y = 
    let id x = x
    in (id id) y;;
val toto : 'a -> 'a = <fun>

Now it works with the normal values:

# toto 5;;
- : int = 5
# toto true;;
- : bool = true

But the identity function returns again the extrange type variables:
# toto (fun z -> z);;
- : '_a -> '_a = <fun>


You can solve this again using the same technique:

# let f y = (toto (fun z -> z)) y;;
val f : 'a -> 'a = <fun>

 
I remember some mail (I think in this list) about this matter. It turs
to be problem with the eta reduction but I don't remind the details, I
remember the solution, to put the varibles in the bindings.

I hope this helps.

Cheers, Juan.

PS. Someone knows the details for this behaviour?